in accordance with Directive 2005/69/EU of the European Parliament and the European Council of 16 Nov. 2005, petroleum plasticizer oils cannot come on the market and be used in the production of tires and their components in the EU since Jan. 1, 2010, if they contain more than 3.0% PCA determined according to the IP-346:1998 method.
Process oils (plasticizers) for butadiene-styrene rubbers and tires having a high content of aromatic hydrocarbons (the content of aromatic carbon more than 25% according to ASTM D 2140) is produced by the method of refining extracts of petroleum oil fractions with selective solvents.
In view of the increased consumption of such plasticizers it is necessary to increase the plant capacity, as well as to improve environmental safety and reduce the energy consumption and other resources for their production.
The currently existing methods of solvent refining of extracts of petroleum oil fractions do not take into account the presence in the extracts of condensed high carbon compounds (carbenes, carboids and the likes), actually insoluble in the majority of known solvents. Such compounds may be present in feed provided at extraction or be formed from using high temperatures in the step of stripping solvents from extraction solutions during the production of extracts, as extracts contain the largest number of reactive compounds (for example, olefins). Insoluble impurities negatively influence the extraction process and decrease the efficiency of operation of plants for producing high aromatic plasticizers. Also there is a need for choosing more selective solvents in order to reduce the number of extracts having a high content of carcinogenic aromatic hydrocarbons.
EP 0417980 is used furfurol as a selective solvent. The refining process is characterized by a low yield of final product (60-70%), low selectivity, inasmuch as furfurol dissolves not only polycyclic but also non-carcinogenic aromatic compounds.
A disadvantage of the known process is the use of a toxic solvent (furfurol) which is also has a high oxidation and resin formation capability.
Known is a method of producing process oils by the two-step extraction method described in DE60013106D.
As a selective solvent furfurol, phenol, N-methylpyrrolidone are used.
A disadvantage of the known process is complexity of the process and toxicity of solvents.
As a polar solvent the use of dimethyl sulphoxide (DMSO) is preferable.
Dimethyl sulphoxide differs from other polar solvents in greater selectivity (correspondingly, the final product yield increases), low toxicity (relates to hazard class 4—a low hazard substance), does not form azeotropic mixtures with water (the process of drying a solvent from water is simplified). The boiling point of dimethyl sulphoxide is at an atmosphere pressure of +189° C., the melting point is +18° C. It is widely used in medicine (cf. “Chemical encyclopedia”, Vol. 2, Moscow. “Sovetskaya entsyclopedia”, 1990, p. 64).
DSMO in all ratios is mixed with aromatic hydrocarbons having no long side chains, and actually does not dissolve paraffin hydrocarbons—this explains its high selectivity towards polycyclic aromatic hydrocarbons and high yield of refined petroleum in refining petroleum extracts.
RU 2313562, cl. C10G21/22, C08K11/00 published on 27 Dec. 2007 is described a process for producing a plasticizer and a plasticizer using dimethyl sulphoxide as an extraction solvent (closest prior art).
The essence of RU 2313562 is in that an extract of refining petroleum oil fractions with selective solvents is treated with dimethyl sulphoxide wherein the dimethyl sulphoxide:extract weight ratio is 2.0-4.0:1 and a temperature range is 30-120° C., and the resulted refined petroleum is used as a desired product. Preferably, the extract is preliminarily diluted with a paraffin-naphthene solvent with a solvent:extract weight ratio of 0.1-0.5:1. The extract is a residual extract and a mixture of residual and distillate extracts.
The invention allows producing a non-carcinogenic aromatic process oil by reducing the content of carcinogenic polycyclic aromatic compounds.
A disadvantage of above process is the use of a paraffin-naphthene solvent which is a highly inflammable liquid reducing thereby the fire-explosion hazard of the process.
Also, the use of a paraffin-naphthene solvent requires lowering the process temperature resulting thereby in increasing the selective solvent:feed ratio and rising energy demands for regenerating the solvent from extraction solutions. Another disadvantage is a hard constraint of water content in the selective solvent—not more than 1%. When a content of water is higher the dissolving capability of dimethyl sulphoxide reduces resulting thereby in increasing the content of carcinogenic polycyclic aromatic compounds. Drying dimethyl sulphoxide to the water content of less than 1% requires for great energy consumption and complicated rectifying equipment.
At the same time at the phase interface level an intermediate layer of insoluble impurities is formed that gradually block the column section resulting thereby in lowering the operation efficiency of the extraction column and breakdown of pump units.
Also these mixtures are partially took away with an extraction solution to evaporating apparatuses wherein the solvent regeneration takes place leading to surface contamination of heat exchanging devices, and as a consequence, a malfunction of evaporators.